Antibody persistence ten years after first and second doses of 23-valent pneumococcal polysaccharide vaccine, and immunogenicity and safety of second and third doses in older adults

In a study of older adults, first and second doses of 23-valent pneumococcal polysaccharide vaccine (PN23) induced IgG increases for all 8 vaccine serotypes tested. Participants (n = 143, mean age 76 y) were re-enrolled to study antibody levels after 10 y, and safety and immunogenicity of another PN23 dose. Ten years after first or second doses, mean IgG concentrations exceeded vaccine-naive levels for 7 of 8 serotypes tested. Second and third doses administered at this time were generally well tolerated and were immunogenic, inducing similar postvaccination levels. Provided that sufficient time is allowed to elapse after each dose, immunogenicity is preserved after multiple PN23 doses without evidence of a lower than expected immune response (i.e., without hyporesponsiveness).